566 THE BEGINNINGS OF LIFE. 



process of fission occurs occasionally even in the very 

 early embryonic stages of higher animals — in which 

 the mass that undergoes the process, save for all its 

 inherited potentialities, differs little from a mass of 

 simplest protoplasm. And again, as we descend in the 

 scale of organization, the lower forms of life are found 

 to retain more and more of those tendencies commonly 

 exhibited by the lowest forms of which they are the 

 more or less remote descendants. Thus fission and 

 gemmation exclusively prevail amongst the ephemero- 

 morphs, and in what is called 'alternate generation' 

 we also meet with such processes occurring most abun- 

 dantly in association with recurring processes of meta- 

 morphosis, of which heterogenesis supplies the originals. 

 The transition, therefore, from the fissiparous mul- 

 tiplication of the germ mass which may take place 

 in the early embryonic stage of man and other 

 mammals, to the multiplication which takes place by 

 a process of internal gemmation in the Aphides, and 

 to those other processes which occur amongst the lower 

 Invertebrata and Cryptogams— constituting the cases 

 of so-called <= alternate generation '—is most gradual 

 and legitimate. This may be seen from the following 

 table, in which some of the principal types of 'alternate 

 generation' have been stated in the simplest manner 

 with the view of facilitating comparison, and thus 

 leading to more comprehensive notions concerning the 

 real nature of the changes which take place and their 

 alliance to other more or less familiar processes : — 



